Search Results (3)

Herein, we investigated the characteristics and mechanisms of interannual variability of extreme summer precipitation in northwest China (NWC). The four high-resolution precipitation predicting products under assessment indicated that both the accumulation of summer daily precipitation ≥95th percentile, and the summer maxima of daily precipitation generally decreased in a southeast—northwest direction, while relatively high values were observed in the Tienshan and Qilian Mountain areas. In turn, the Tropical Rainfall Measuring Mission (TRMM) satellite dataset underestimated extreme precipitation in mountainous areas, while Asian precipitation highly—resolved observational data integration towards evaluation (APHRODITE) and Climate Prediction Center (CPC) captured the characteristics of extreme precipitation in NWC. AMIP-type simulations of the interannual variability of extreme summer precipitation in NWC were quite unsuccessful. However, all of them can capture the increasing trends. Therefore, we further found that the interannual increase in extreme precipitation in NWC is strongly correlated with the weakened South Asian high, strengthened Western Pacific Subtropical high, the enhanced westerly jet, and the mid- to high-latitude Rossby wave trains, whose formation and sustenance can be traced back to sea surface temperature-anomalies in the western Pacific in May, June, and July. An increased sea surface temperature promotes convection and induces diabatic heating, which stimulates anticyclonic anomalies that disturb the enhanced westerly jet, resulting in a barotropic Rossby wave train via the Gill-type response. Additionally, it guides more water vapor convergence to NWC and enhances upward motion via anticyclonic anomalies over western Europe and Eastern Asia, and cyclonic anomalies over Central Asia. Full article

Natural and social environment changes have played important roles in social evolution in different times and spaces. Geopolitical change, in particular, might play a decisive role in social evolution during historical periods. The eastern Tienshan Mountains was a transportation hub for communication between the East and the West, where the natural environment is fragile and the social environment has been complex during the historical period. However, geopolitical change and its impact on local social development remain unclear due to fragmented historical records and limited studies. This study investigates the spatiotemporal variations of military facilities in the Hami region, and compares historical documents and archaeological and paleoclimate records to discuss geopolitical changes and social evolution during the historical period in the eastern Tienshan Mountains. A total of 84 visible organic remains from 38 historic beacon towers and 8 dak sites in the Hami region of the eastern Xinjiang Uygur Autonomous Region, northwestern China, were collected and the radiocarbon (¹⁴C) dates of these ruins were systematically determined with accelerator mass spectrometry. The dating results show that these sites were mainly built during two major periods: ca. 600–900 cal AD and ca. 1600–1950 cal AD, which roughly correspond to the Tang Dynasty (618–907 AD) and the Qing Dynasty (1636–1912 AD) in ancient China. Human settlement intensity was high during the Han, Tang, and Qing dynasties, and relatively low when the area was controlled by nomadic or local regimes. This suggests that agricultural empires and nomadic/local regimes adopted different strategies for regional management. Climate change might have affected geopolitical patterns, which, in turn, profoundly influenced human activities and social evolution in the eastern Tienshan Mountains over the last two millennia. This study systematically reveals the spatiotemporal variations of beacon towers and dak ruins in the region through a large number of reliable direct ¹⁴C dating, it reveals the remarkable differences in human activities in the eastern Tienshan Mountains under different administrations, and it explores the influence of geopolitics and climate change on social evolution in the eastern Tienshan Mountains from a multidisciplinary perspective. Full article

Glacier melting is one of the important causes of glacier morphology change and can provide basic parameters for calculating glacier volume change and glacier mass balance, which, in turn, is important for evaluating water resources. However, it is difficult to obtain large-scale time series of glacier changes due to the cloudy and foggy conditions which are typical of mountain areas. Gravity-measuring satellites and laser altimetry satellites can monitor changes in glacier volume over a wide area, while synthetic-aperture radar satellites can monitoring glacier morphology with a high spatial and temporal resolution. In this article, an interferometric method using a short temporal baseline and a short spatial baseline, called the Small Baseline Subsets (SBAS) Interferometric Synthetic-Aperture Radar (InSAR) method, was used to study the average rate of glacier deformation on Karlik Mountain, in the Eastern Tienshan Mountains, China, by using 19 Sentinel-1A images from November 2017 to December 2018. Thus, a time series analysis of glacier deformation was conducted. It was found that the average glacier deformation in the study region was −11.77 ± 9.73 mm/year, with the observation sites generally moving away from the satellite along the Line of Sight (LOS). Taking the ridge line as the dividing line, it was found that the melting rate of southern slopes was higher than that of northern slopes. According to the perpendicular of the mountain direction, the mountain was divided into an area in the northwest with large glaciers (Area I) and an area in the southeast with small glaciers (Area II). It was found that the melting rate in the southeast area was larger than that in the northwest area. Additionally, through the analysis of temperature and precipitation data, it was found that precipitation played a leading role in glacier deformation in the study region. Through the statistical analysis of the deformation, it was concluded that the absolute value of deformation is large at elevations below 4200 m while the absolute value of the deformation is very small at elevations above 4500 m; the direction of deformation is always away from the satellite along the LOS and the absolute value of glacier deformation decreases with increasing elevation. Full article